Molecular sieves are a commercially important class of crystalline materials. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species.
Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework type zeolites and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the “Atlas of Zeolite Framework Types,” Sixth Revised Edition, Elsevier (2007).
One known molecular sieve for which a structure has been established is the material designated as TON, which is a crystalline material having one-dimensional 10-membered ring channels. Examples of TON-framework type molecular sieves include ISI-1, KZ-2, NU-10, Theta-1 and ZSM-22. TON-framework type materials are of significant commercial interest because of their activity as catalysts in dewaxing of paraffinic hydrocarbons.
Borosilicate molecular sieves can be of interest when a molecular sieve of reduced acidity is desired. A borosilicate molecular sieve having the TON-framework type is reported to have been hydrothermally synthesized using a 1,3-dimethylimidazolium cation as the structure directing agent, but the synthesis requires the presence of concentrated hydrofluoric acid. See R. H. Archer et al., Micropor. Mesopor. Mater. 2010, 130, 255-265. An amorphous material was produced from a borosilicate hydroxide-mediated reaction gel when a 1,3-dimethylimidazolium cation was used as the structure directing agent.
The use of fluoride in molecular sieve reaction gels is undesirable on a large scale because of the potential hazards involved. There thus remains a need for a method of synthesizing borosilicate TON-framework type molecular sieves that eliminates the need for a source of fluoride.